Magnetic resonance imaging (MRI) is a non-destructive method for the analysis of materials and represents a relatively new approach to medical imaging. It is generally non-invasive and does not involve ionizing radiation. In very general terms, nuclear magnetic moments are excited at specific spin precession frequencies which are proportional to the local magnetic field. The radio-frequency signals resulting from the precession of these spins are received using pickup coils. By manipulating the magnetic fields, an array of signals is provided representing different regions of the volume. These are combined to produce a volumetric image of the nuclear spin density of the body. More specifically, nuclear spins can be viewed as vectors in a three-dimensional space. During an MRI process, each nuclear spin responds to four different effects—precession about the main magnetic field, nutation about an axis perpendicular to the main field, and both transverse and longitudinal relaxation. In steady-state MRI processes, a combination of these effects occurs periodically.
It would be desirable to have a method for spectrally selective imaging of different resonances that is specifically designed to both preserve hyperpolarized magnetization in a substrate while providing higher signal-to-noise-ratio (SNR) signals of metabolic products of the substrate.